Electroluminescent elements such as organic EL elements and LED's are of a structure in which electrode layers, light emitting layers and the like are laminated on a substrate. Commonly, light emitted within a light emitting layer is output through a transparent electrode. At this time, light which enters an interface between layers at a critical angle or greater is totally internally reflected and trapped within the element, due to the influence of the refractive index of each layer, and is not output. For this reason, it is difficult for emitted light to be output efficiently. In the case of ITO, which is commonly used as a transparent electrode, the refractive index thereof causes output efficiency to be approximately 20%. Accordingly, improvement of the light output efficiency of electroluminescent elements is a major problem to be solved.
Techniques for effectively causing the totally internally reflected light to be output are being considered with respect to this problem. For example, a technique has been proposed in which the light output efficiency is improved by providing a diffraction grating at an interface between layers at which light is totally internally reflected. In this technique, the diffraction grating changes the optical path of light that enters the interface at an angle greater than or equal to a critical angle. Thereby, the incident angle of the light becomes less than or equal to the critical angle, and the light can be output.
Japanese Unexamined Patent Publication Nos. 2006-221976 and 2006-236748 disclose organic electroluminescent devices in which diffraction gratings are provided at interfaces at which total internal reflection occurs. These organic electroluminescent devices achieve improvement of light output efficiency by reducing view angle dependency, which is a problem to be solved by the diffraction gratings with respect to light output, by varying the pitch and pattern of the diffraction gratings.
However, in the organic electroluminescent devices disclosed in Japanese Unexamined Patent Publication Nos. 2006-221976 and 2006-236748 that change the optical paths of totally reflected light with the diffraction grating to output the light, the improvement in brightness is 1.2 to 1.7 times, which is not sufficient. In addition, the diffraction gratings are formed mainly by etching and the like. Therefore, in structures that output light from the side opposite substrates (top emission type), there is a possibility that electrode layers and light emitting layers will become damaged when forming the diffraction gratings.
The present invention has been developed in view of the foregoing circumstances. It is an object of the present invention to provide a light emitting element that outputs emitted light through a transparent electrode having highly efficient light output, which is capable of being produced without damaging electrode layers or a light emitting layer.